Before we get too excited, I wouldn't neccessarily chalk this one up soley to corrosion. Its hard to tell from the pics, but it looks like the spoke was a few mm's short which puts the nipple purely in tension. Ideally (from what I've read ), the spoke should protrude past the plane where it seats in rim so that it's loaded in both compression and tension. Looks like a tensile failure to me. Whether or not corrision was a contributing factor is debateable. Also very well possible that you got a couple of bad nipples.

Meltingfeather, call me out if I'm wrong here.

Interesting. When I looked at the other broken spokes, they look like they broke around the pretty much the same spot on the nipple. Looking into the the spoke holes from the rim bed, some of the unbroken ones are protruding well into the nipple and others are recessed into the nipple.
So, this could be a combination of a bad build and corrosion.
i will try a different bike shop for the next build.

I was looking for info on the question of whether silver DT nipples are anodized, and found some interesting info (or perhaps "claims") from Sapim:

In the past, aluminum nipples had only one positive argument, the weight. All other features like corrosion resistance, friction, stiffness were specific to brass nipples. This changed in the last years drastically. All our aluminum nipples are now anodized. Salt spray tests showed better results than brass nickel plated nipples. You can choose 7 different colors. We had been able to reduce friction with a special coating. As an effect you don’t need to oil or grease the nipple like you should with the brass version. For the last three years, Sapim has used the 7075 material and have additional strength added by the heat treatment T6. Alloy nipples are now stronger than brass. Aluminum nipples are more expensive but for sure much better than brass. For those who care about weight, special colors and quality, aluminum nipple is advised.

That doesn't sound right. Bare aluminum develops a thin oxide film, but anodizing makes a much thicker protective layer. You seem to be suggesting that letting bare aluminum sit in air will achieve the same effect. That is definitely not correct.

I'm very surprised if that's true that silver DT nipples are not anodized.

You're right on the thickness between the natural and artificial processes. However, thickness notwithstanding, aluminum will oxidize and "ano" itself.
Now, if you pair this w/ heat treating, a hardened aluminum part with an artificially ano'd surface will be a more durable part than an identical part w/o artificial ano-ing.
My point: it doesn't really matter if a nipple is or isn't ano'd. Check the 4th paragraph on the thickness of the artificially ano'd part, and think about how much material is removed during the wheel's tension phase during a build: The Fundamentals of TIG Welding Anodized Aluminum

Edit: I'm pretty certain that even w/ lube, the amount of aluminum removed during tensioning will be an order of magnitude or two more than the artificially ano'd thickness.

Interesting. When I looked at the other broken spokes, they look like they broke around the pretty much the same spot on the nipple. Looking into the the spoke holes from the rim bed, some of the unbroken ones are protruding well into the nipple and others are recessed into the nipple.
So, this could be a combination of a bad build and corrosion.
i will try a different bike shop for the next build.

SO much motivation for me to rebuild my wheels w/ brass now!
Recall me mentioning the "heavier" rim seems to have added enough thickness to the ERD to add another millimeter to the calc'd spoke length...used 292, but would rather have gone w/ 293...?

So the anodizing is 0.005-0.025mm thick, and you're saying the tensioning process removes 10-100 times that amount. Are you using a bench grinder to tension your wheels?

Personal experience:
I've disassembled a wheel I started w/ some blue ano'd alloy nipples (wrong spoke length...too long). Where the nips contacted the stainless eyelet, a silver ring of bare alum sat, and this was w/ TriFlo lubed threads and nipple/seat.

The surface may be harder, but the alum under is soft and will give. And when it does, you take off cracked ano'd layer along w/ some of the soft stuff...even if heat treated.

And, let's put those numbers in perspective...at the most extreme end...
0.025mm is 2.5% of a millimeter. Obviously, 100 times this thickness isn't right...actually about the diameter of the spoke itself, yeah? BUT, at 10x, that's only 25% of one mm. Does that sound reasonable?
For the smaller number...0.005, 100x is 1/2mm, and 10x is 1/2 of 1% of a mm. I can totally see this amount being worn off...albeit 1/2mm would be pretty severe!

Personal experience:
I've disassembled a wheel I started w/ some blue ano'd alloy nipples (wrong spoke length...too long). Where the nips contacted the stainless eyelet, a silver ring of bare alum sat, and this was w/ TriFlo lubed threads and nipple/seat.

Were they DT nipples? The more I look into it, the more I wonder if DT alloy nipples are anodized at all, regardless of colour. Wheelsmith and Sapim both explicitly advertise their nipples as anodized, but DT makes no mention of it at all. Perhaps they are raw aluminum with some sort of dye for the coloured versions.

The quote above from Sapim says "All our aluminum nipples are now anodized", implying that they weren't before? So maybe it's not that unlikely that DT nipples are still not anodized.

Were they DT nipples? The more I look into it, the more I wonder if DT alloy nipples are anodized at all, regardless of colour. Wheelsmith and Sapim both explicitly advertise their nipples as anodized, but DT makes no mention of it at all. Perhaps they are raw aluminum with some sort of dye for the coloured versions.

The quote above from Sapim says "All our aluminum nipples are now anodized", implying that they weren't before? So maybe it's not that unlikely that DT nipples are still not anodized.

Yeah, they were. Also on red ones...and black ones.
I'm not sure how you can lay down a layer of color w/o at least some form of ano-ing...tho I guess something like a Sharpie...

Ya know... the thought of heat treating kinda just popped into my head about Gunnar's snapped nipple. If DT does it, and on the occasional situation where cooling was too fast, there could very well been an especially brittle nipple...but totally e-speculation on my part tho.

anodizing and color dying are two different processes. I don't know how 'deep' the dye goes into the ano layer. In order to dye an aluminum part, it must be anodized then dipped in a dye tank. Silver ano is not dyed. I know that black requires a thicker ano layer for the dye to take well. Lighter colors require less ano thickness to take the dye. True black is the most difficult. Maybe some expert on anodizing can chime in on the thickness that the ano dye is absorbed into the ano layer. It may be possible for an anodized/dyed nipple to show silver at the rim/nipple interface without exposing the non-anodized portion of the aluminum, if that makes sense. All I know is from my home anodizing setup for bike light bodies. Again, I am no expert.

Fat Biker - Can''t help you find the A2Z hubs but bikehubstore.com has Rotaz and Bitex hubs available - they should be comparable to the A2Z's. I'm going to go with the Bitex hubs - just over 400grams a set, $150, available in thru axle or QR.

Now you guys can quit beating me up for suggesting this could be a problem. Anodized should help a lot, but I still think that down the road as the anodizing wears off this will be a problem. The ENVE rims have molded spoke holes so the carbon is covered up.
Since I didn't really consider this problem until the question was asked on this forum, I took no precautions with my first 2 sets I built. With this last set, I dipped a chopstik in a can of the copper colored never seize and poked it through each spoke hole before I built the wheels. In a couple of years I will be able to tell you if this helped.

Yes. Originally I wasn't expecting them until after Feb 20 (as per Brian) but I got an e-mail last might stating that they shipped (along with a tracking number). They must have started the 29er wide rims earlier than anticipated.

Re: (Cheap) Chinese Carbon Rims?

Please post pics and impressions when you get them in...I am looking at getting a set and would love to know if there are improvements in the new process.

Thanks

Originally Posted by botanicbiker

Yes. Originally I wasn't expecting them until after Feb 20 (as per Brian) but I got an e-mail last might stating that they shipped (along with a tracking number). They must have started the 29er wide rims earlier than anticipated.

I have a pair of 700c road rims that bulged after my first descent. "Nancy" said that this was a known problem and they could warranty them no problem. I explained that I no longer could trust their road rims, but had heard good things about the wide 29er rim. She said, "no problem, but our production is delayed and it may take several weeks" This took place back in August and she kept feeding me this same line for several months and then disappeared. Last I heard from her was in November. Any tips for dealing with LB? Thanks for the help!

Ok been wondering where to post this, but since so many wheel builders appear to frequent this thread, and I do have these carbon rims, I will ask here.

Not sure what spoke lengths to choose, given the calculator output vs the available sizes of DT Revolution which are in 2mm increments.

The only recommendation I came across is to round down the values coming from the spoke length equation, which the calculator already did, but to arrive at the nearest stock length seems to me a bit of a stretch in a few cases, which I'm thinking might be better to do a smaller jump in the opposite direction (e.g. make the spoke 0.1mm longer instead of 1.9mm shorter.

(I know I can get these shortened and rethreaded in some shops, but I'd prefer to avoid that, conjuring the spoke is strongest/fittest when it's not tampered with after the initial manufacturing process.)

So the pic of the sheet lists differences from the available stock spokes (which are 290, 292 and 294mm), where positive number means that much shorter spoke (than the one calculated).

Simply getting the 292mm would simplify things for me in terms of stocking/replacements, but I'm not sure about getting the "rear right" spokes almost 1mm longer than what the calculator printed.

Those spokes are available in every length, not just 2mm increments. I built my light-bicycle wheels with a combination of 291, 292 and 293. It would be best to buy the exact length needed, although people do get by with spokes that are off by 1mm.

Looking at the picture you attached. for the front, I think you would need 292mm for the left and 294 for the right. I read some where that spoke length could be + or - 1 mm of calculated length. So you should round up or down to get to the nearest length available. In this case, 294 is within 1 mm of 293.5 whereas 292 is 1.5 mm so 294 would be the better choice. 292 for the back looks ok to me(but I'm just a noob and only built up 3 sets of wheels so far so you might want to wait for other more experienced members to chime in)

Revolutions come in 1mm increments, I used them on my last build. General wheelbuild practice is to round down from whatever the exact calculation is. I am not sure of the origin of this practice, it was taught to me by the person that taught me to build wheels. I think the calculators calculate the spoke length to about the bottom of the nipple and all you really need is some of the thereads into the base of the nipple so rounding down works.